ABSTRACT
Up to this point in our treatment of regression analysis, we have been working with explanatory variables whose values are explicitly defi ned on some unambiguous scale of measurement, e.g., variables such as disposable income per year, retail sales fi gures per month, man hours worked per week, elapsed time in minutes, distance traveled in miles per day, etc. Note that all of the aforementioned variables are quantitative: they are measured on a numerical scale, with a defi nite positional ordering existing among the observed values of the variable.
